(551f) Surface Tensions of Organophosphorus Compounds.

While production and stockpiling of organophosphorus chemical warfare agents (CWAs), such as sarin, have been banned three decades ago, they remain a threat. New approaches to decontamination and destruction of CWAs motivate studies of their physico-chemical properties. Since CWAs often present in the form of aerosols, the surface tension of liquid CWAs is one of the key properties.

Due to the extreme toxicity of CWAs most experimental studies are carried out with surrogates -- organophosphorus compounds which, while having similar structures, are much less toxic, e.g. dimethyl methylphosphonate (DMMP) and diisopropyl methylphosphonate (DIMP). Nonetheless, previously reported data on surface tensions of sarin and surrogates are very scarce.

In this work, we consider two methodologies, experimental measurement and molecular dynamics simulation, to obtain the surface tension of organophosphorus compounds, such as DIMP and DMMP, in the range of temperatures from 0℃ to 60℃. The experiment was performed using the droplet weight method, and simulation was done using molecular dynamics with a TraPPE (Transferable Potentials for Phase Equilibria) force field. The predictions for DMMP agreed well with our experimental data, and for DIMP the agreement appeared perfect, which justified the predictive capability of our approach. Consequently, we applied the TraPPE force field to predict the surface tension of sarin in a wide range of temperatures. Thus, the main goal of this work is to show that our study provided the surface tension data for sarin and its surrogates, which can be used in the predictive models for studying their aerosols. They further justified using the TraPPE force field for predicting the thermodynamic properties of organophosphorus compounds.